Maintainance mode for cdk-nag for CDK v1 and monocdk

[dontirun]

cdk-nag will enter maintenance mode for CDK v1 and monocdk on June 1st, following the AWS CDK timeline for deprecating CDK v1 support. No new rule, features, or fixes will be added to cdk-nag for CDKv1 and monocdk starting at that time.